Electrical resistance element

ABSTRACT

An electrical resistance element formed of an array of parallel MoSi2 rods coupled in series by connecting adjacent rod ends together in pairs at one end of the array and at the other end connecting adjacent rod ends together in pairs staggered with respect to those at the first end. The connection is made by means of a flame-sprayed layer of MoSiAl or MoSi2 and the array is supported by an elastic cross bar in a ceramic frame.

United States Patent [151 3,668,599

Schrewelius. 1 June 6, 1972 [54] ELECTRICAL RESISTANCE ELEMENT 737,6899/1903 Win ..33s 2s9 1,657,507 1/1928 Keene... ..338/295 [72] Inventor.lSQilsdGustav Schrewelius, Hallstahammar, 1,719,179 7/1929 Haydenm""338,3 1 8 x we 1,861,434 6/1932 'CampbelL. .....338/318 x 73 Assignee;Akfiebolgge' m Hansgahammar, 2,992,959 7/1961 Schrewelius. .....338/330X Sweden I 3,144,545 8/1964 Shrimplin ..219/532 X 1 3,321,727 5/1967Schrewelius ..338/330 [22] Filed: Sept. 15, 1970 v [21] APPL No; 72,454Primary Examiner-E. A. Goldberg Anorney--Brumbaugh, Graves, Donohue &Raymond [30] Foreign Application Priority beta I l t [57] ABSTRACT Sept.16, 1969 Sweden 12710/69 A le tri l re i tance element formed of anarray of parallel MoSi rods coupled in series by connecting adjacent rodends [52] U.S. Cl. ..338/289, 338/318, 219/532 together in pairs at oneend of the array and at the other end [51] Int. CL... H010 1/02connecting adjacent rod ends together in pairs staggered with [58] Fieldof Search ..338/295, 289, 318, 330, 332, respect to those at the firstend. The connection is made by 338/315, 316, 317, 319, 320; 219/532means of a flame-sprayed layer of MoSiAl or MoSi and the array issupported by an elastic cross bar in a ceramic frame. [56] ReferencesCited v UNITED STATESPATENTS v I 5 Claims, 1 Drawing Figure 497,7955/1893 Jenkins ......338 /295 i 4 l ELEc'rRrcAL RESISTANCE ELEMENT .Thepresent invention relates to an electrical resistance element of thekind having a resistance conductor of a material brittle in coldcondition, particularly molybdenum disilicide.

Electrical resistance elements, particularly intended for translucentcooking plates have been previously proposed, comprising resistanceconductors of a material brittle in cold condition, e.g., the materialsold under the registered trade mark KANTHAL Super. Said materialconsists essentially of molybdenum disilicide. In these known elementsspirals, meanders or other shapes have been used in which a long, ratherthin wire of said material has been shaped in heated condition to adisc-like element. The disc-like resistance element has been placed on afire resistant support, such as a mineral fiber plate. However, it hasbeen found that the support hascaused corrosive attacks on theresistance material, and particularly the shaping, the transportationand the mounting of the disc-like resistance elements have involvedgreat problems. i

. The object of the present invention is to provide an electricalresistance element in which said problems have been avoided and for thispurpose the resistance element according to theinvention ischaracterized in that the resistance conductor consists of a pluralityof substantially straight elements disposed in a common plane andconnected in series by having their ends connected to each other inpairs at staggered positions on respective ends of the element to form aresistance conductor of the required length.

; .The invention will be described below with reference to theaccompanying drawing which shows a top view of a resistance elementchosen as anexample only. g

'In the embodiment shown,'the resistance element consists I of'aplurality of substantially straight parallel element rods connected inseries by having their ends connected in pairs at one end and,'at theother end, in pairs staggered with respect In the example, the elementrods 10 are connected elastically or resiliently to a rigid support,which in this case consists to thepairs on the first end so as to form aresistance conduc- 1 tor of the required length. The ends of the elementrods are connected with each other by means of a flame sprayed layer 11of MoSiAl or Mosi for example, The element rods 10 are interconnectedmechanically, but not electrically by means of two transverse bars l2,e.g., ofAl O The two transverse bars 12'also resilient connect theelement rods 10 to a rigid sup-' port,in this case a frame 13 enclosingthe element and consisting of A1 0 The ends of the two outermost rodsare connected to rather thick lead-in wires 14, 15 of metal, saidleadin, wires being connected with the ends of the element rods by meansof flame sprayed layers of Mosi for instance.

K In the example shown, the-element rods 10 are arranged in a paralleland rather closely spaced array. in most cases this arrangement will bepreferable, but it is also possible to arrange the essentially straightelement rods in some other configuration to form a plate. Further, allthe element rods are interconnected in that the ends of pairs ofadjacent rods 10 are connected with each other and with the ends ofadjacent rods,

respectively, in such a way that the element rods connected in seriesfonn a continuous resistance conductor. Of course, it is also possibleto make the connection in such a way that on each separate occasion onlya portion of the disc-like element is switched on and the connection mayalso be made such that when using three-phase current the element isoperated either in Y-connection or in A-connection.

In the embodiment shown, all the element rods 10 are equal length sothat a square resistance element (as seen in top view) is obtained.However, for some practical applications it will of course be possibleto chose rods with a length progressively increasing from one side ofthe element towards the middle and then progressively decreasing so thatthe shape of the element plate as'a whole is approximately circular, asseen from above. i

in the example, the connecting layers 11' which are staggered from oneend to the other are created by masking spaces 16 between the rod ends,when flame spraying.

of a frame 13 of, e.g., Al o -ceramics enclosing the element. In thiscase, the connection has been provided by extending the sprayed-on thincross connections 12 between the element rods to the enclosing frame. Ofcourse, it is also possible to use some other kind of rigid support,such as a supporting plate which may also be designed as a reflector, ifrequired.

As in the example shown, the lead-in wires 14, 15 may be drawn throughthe frame at one side of the element. However, it is equally wellpossible to draw the lead-in wires through the bottom of a plate-shapedsupport, for instance, and to supplement said plate-shaped support by atranslucent casing, for example, of some suitable material so that theunit thus formed is useful as a cooking plate of approximately theconventional kind. In the embodiment shown, the intention is that itshould be possible to place the element under a glass plate at anappropriate distance therefrom, in which case no separate support orbottom insulation under the cooking plate is required.

Conveniently, an element according to the invention may have the outsidedimensions 150 X 200 X 2 mm, and the resistance element rods may have adiameter of 0.5 mm.

Of course, the cross connection material is chosen such that thematerial does not react with the resistance material of the elementrods, and further the cross connections must be such that the element'issufficiently resistant to high temperatures so that it does not becomedeformed when used. In case the element rods consist of molybdenumdisilicide, as is particularly preferred according to the invention, itis advisable to use aluminum oxide for the sprayed-on cross connectionbeads, as the aluminum oxide does not react with the resistance materialmentioned. Owing to the design of the element,'the individual elementrods 10 can, to a considerable extent, move freely at variations intemperature. i-lowever,also in cold condition the element issurprisingly insensitive to impacts which is probably due to the factthat-the element is flat andthin so that it becomes surprisinglyelastic.

It should be apparent that the costs of manufacture for elements of thekind now proposed become very low, as all the steps in the production ofthe element can be automatized.

A great many modifications and alterations of details are possiblewithin the scope of the inventive idea.

What is claimed is:

l. Anelectrical resistance element, comprising:

a plurality of elongated resistance rods formed of a resistance materialwhich is brittle in cold condition;

. electrical interconnection means between said rods for connecting saidrods in a continuous series circuit; and

- resilient support means for resiliently holding said rods in a spacedarray, said support means including a resilient cross bar formed ofdielectric material interconnecting all of said rods intermediate theends thereof.

2. An electrical resistance element as claimed in claim 1, furthercomprising:

frame means surrounding said resistance rods, said resilient cross barconnected at opposite ends thereof to said frame means.

3. An electrical resistance element as claimed in claim 2, wherein saidspaced array of said rods includes a plurality of substantially straightmutually parallel element rods connected in series by having their firstends connected in pairs and their other ends connected in pairsstaggered by one rod with respect to the pairs at said first ends.

4. An electrical resistance element as claimed in claim 3 wherein saidresilient support means includes two spaced parallel resilient crossbars supporting all of said rods at symmetrical positions spaced fromthe ends of said rod, approxiflame sprayed layer of a material includingmolybenum disilicide.

t in s t s

2. An electrical resistance element as claimed in claim 1, furthercomprising: frame means surrounding said resistance rods, said resilientcross bar connected at opposite ends thereof to said frame means.
 3. Anelectrical resistance element as claimed in claim 2, wherein said spacedarray of said rods includes a plurality of substantially straightmutually parallel element rods connected in series by having their firstends connected in pairs and their other ends connected in pairsstaggered by one rod with respect to the pairs at said first ends.
 4. Anelectrical resistance element as claimed in claim 3 wherein saidresilient support means includes two spaced parallel resilient crossbars supporting all of said rods at symmetrical positions spaced fromthe ends of said rod, approximately one-fourth the length thereof.
 5. Anelectrical resistance element as claimed in claim 3, wherein saidelectrical interconnection means comprises a flame sprayed layer of amaterial including molybenum disilicide.